Adobe introduced the public beta of Adobe Lightroom, an all-new digital imaging solution for professional photographers. With its modular, task-based and streamlined environment, Lightroom's goal is to deliver a complete photography workflow. As Adobe collects more feedback from photographers, modules and feature sets will likely change, as customers decide on their popularity and priority within digital photography workflows. Initially available as a beta for Macintosh, Lightroom will later support both the Windows and Macintosh platforms. UPDATE by ELQ: Previews here, here and here. It seems that Lightroom reads RAW images correctly and it has Curves support, compared to Aperture.

MacWorld is running an article on it. The interfaces can be written for Cocoa via ObjC++ but the main bulk of the application can be written in C++ and not be difficult to port with different interfaces for Windows.